Environmental safety apparatus for airborne hydrogen fluoride recovery and method

ABSTRACT

A safety apparatus has been found for recovering an airborne hydrogen fluoride release in a hydrocarbon alkylation process. The safety apparatus comprising containment baffles and hydrogen fluoride detectors. Hydrogen fluoride detectors activate water flood means which discharge into the containment baffles. The water flood containing essentially all of the hydrogen fluoride release is recovered for disposal. Recoveries of 90 wt % have been demonstrated.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to Ser. No. 07/944,619 filed Sep. 14, 1992,for Hydrogen Fluoride Alkylation Apparatus and Vapor Recovery Method toG. P. Partridge, Jr.; K. R. Comey, III; J. Mudra IV and L. K. Gilmer nowU.S. Pat. No. 5,277,881.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is an environmental safety apparatus in combination withmeans for using hydrogen fluoride. The invention is also a safety methodof collecting an airborne release of hydrogen fluoride.

2. Description of the Related Art

The catalytic alkylation of an isoparaffin with an olefin to produce abranched paraffin is a commercially important process for producing highoctane gasoline. In general, the process comprises the reaction of anisoparaffin such as isobutane with an olefin such as propylene,1-butene, 2-butene or mixtures thereof in the presence of a liquid acidalkylation catalyst in a reaction zone. Reaction is followed byseparation of the product and unreacted hydrocarbons from the liquidalkylation catalyst in a settling zone and purification of the alkylateproduct. If the isoparaffin is isobutane and the olefin is a butene, thealkylate product is isooctane. Alkylate product is used to enhance theoctane number of automotive gasoline and aviation gasoline.

Anhydrous hydrogen fluoride is a particularly effective catalyst for thealkylation process. Though effective, the volatility and destructiveeffect of hydrogen fluoride on animal tissue has curtailed expanded useof this catalyst in the petroleum refining industry due to a concernover accidental releases.

There is a need in the petroleum refining industry for an apparatus andmethod which will contain an accidental release of hydrogen fluoridefrom a major process vessel.

SUMMARY OF THE INVENTION

The invention is an environmental safety apparatus for collecting anairborne release of hydrogen fluoride from a hydrogen fluoride utilizingmeans.

The environmental safety apparatus comprises a containment baffledefining a volume sufficient to substantially enclose the utilizingmeans. At least one hydrogen fluoride detecting means is mounted withinthe containment baffle. Flood means has a capacity to substantiallyflood the containment vessel with an aqueous liquid. Means is providedresponsive to detecting means to activate the flood means. Means isprovided to receive the aqueous liquid from the containment baffle.

The invention is used in combination with hydrogen fluoride utilizingmeans such as an alkylation process vessel, containment vessel ortransportation vessel to capture an accidental airborne release ofhydrogen fluoride. As a result, escape of the release is prevented anddamage to the environment is prevented.

BRIEF DESCRIPTION OF THE DRAWING

The Drawing is a schematic flow diagram illustrating a preferredembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The alkylation reaction is carried out between an isoparaffin and amonoolefin in the presence of alkylation catalyst. The preferredisoparaffin is isobutane. Isopentane is also used. Common monoolefinsinclude propylene, isobutylene, 1-butene, 2-butene, pentylenes andmixtures thereof. The preferred monoolefin is a C₄ olefin, typically amixture of 1-butene, 2-butene and isobutene. A typical C₄ olefin mixtureis one fraction from a fluid catalytic cracking process comprising about25 vol % 1-butene, 45 vol % 2-butene and 30 vol % isobutylene. Diolefinsor higher functionality olefins are to be avoided in the reaction.Higher functionality olefins alkylate at each double bond, formingpolymers which are not useful for gasoline blending.

The alkylation catalyst is hydrogen fluoride, referred to in the art ashydrofluoric acid or simply by its molecular symbol HF. Generally,anhydrous hydrogen fluoride is supplied to the process. In use, atypical analysis shows 1 wt % to 2 wt % water and 5 wt % to 15 wt % acidsoluble oil.

The reaction may be carried out at pressures varying from atmospheric toas high as 1000 psia (68 atm) or higher, preferably about 125 to 220psia (8.5 to 15 atm) and at residence times of 20 seconds to 5 minutes.The pressure is selected in cooperation with the temperature to maintainthe hydrocarbon reactants in liquid phase and generally ranges from −40°F. (−40° C.) to about 150° F. (66° C.). In the preferred reaction ofisobutane with a C₄ monoolefin the reaction temperature is between about60° F. (15° C.) and about 100° F. (38° C.) and most preferably about 90°F. (32° C.).

In the alkylation reaction a substantial molar excess of isoparaffin toolefin is employed to provide an isoparaffin/olefin feed ratio in excessof about 1/1, generally 4/1 to 70/1 and preferably 5/1 to about 20/1.

Reference is made to the Drawing. The isoparaffin feed in line 24 andthe olefin feed in line 25 are combined and introduced into reactorvessel 30 via lines 26, 27 and 28. Fresh, anhydrous hydrogen fluoride intank 10 is passed via line 17 into reactor vessel 30 which is eitherhorizontally or vertically elongated and cylindrical in shape. Thevolume of anhydrous, liquid hydrogen fluoride exceeds the volume of theisoparaffin and monoolefin mixture. The liquid hydrogen fluorideconstitutes a continuous phase in reactor vessel 30 and the hydrocarbonfeedstocks constitute a discontinuous phase. Coolant, such as coolingwater is passed via line 21 through heat exchanger tubes (not shown)exposed to the reaction mixture in reactor vessel 30, thereby moderatingreaction temperature to the selected range. Coolant is discharged vialine 22.

Reaction effluent, comprising alkylate product, unreacted isoparaffinand liquid catalyst are withdrawn from reactor vessel 30 via line 34 anddischarged into catalyst settler vessel 50 which is vertically elongatedand cylindrical in shape. The catalyst settler vessel 50 allows forseparation of the reaction effluent from the alkylation reactor into anupper liquid hydrocarbon phase and a lower liquid catalyst phasecontaining hydrogen fluoride catalyst, acid soluble oil, and water. Thecatalyst settler vessel 50 may contain separation trays and verticaldowncomers (not shown) positioned within the vessel to enhanceseparation.

The alkylate product phase is withdrawn via line 57 and processed byfractional distillation (not shown) to recover unreacted isoparaffin andalkylate product.

The liquid catalyst phase is withdrawn via line 60 and passed to spentacid tank 70. A portion of this acid may be recycled (not shown) fromspent acid tank 70 to reactor vessel 30.

Surrounding and enclosing each of the major process vessels is acontainment baffle. The containment baffle allows for a vapor spacebetween the vessel and the baffle. Fresh acid tank 10 is enclosed bycontainment baffle 12, providing vapor space 11 and fluid communicationwith the air via slots 12s. Reactor vessel 30 is enclosed by containmentbaffle 32, providing vapor space 31 and fluid communication with the airvia slots 32 s. Acid catalyst settler 50 is enclosed by containmentbaffle 52, providing vapor space 51 and fluid communication with the airvia slots 52 s. Spent acid tank 70 is enclosed by containment baffle 72,providing vapor space 71 and fluid communication with the air via slots72 s.

Each of the vessels is cylindrical in shape as is each containmentbaffle. Preferably each containment baffle has a cylindrical radius 0.25inches (0.635 cm) to 36 inches (91.44 cm) greater than the cylindricalradius of the vessel. Should a major process vessel leak, the vaporspace provides volume for hydrogen fluoride to collect while limitingescape to the atmosphere via the slots. Hydrogen fluoride vapor at aninitial escape velocity of 50 ft./sec. to 1500 ft./sec. has been foundto condense on the baffle at atmospheric temperature and pressure,forming a vapor-condensate mixture.

The containment baffles dissipate the momentum of the escaping hydrogenfluoride vapor and reduce the velocity of the vapor-condensate mixtureto that of the ambient air or less, generally 0 to 15 miles/hr. (22ft./sec.), typically 0 miles/hr (0 ft./sec.) to 5 miles/hr. (7.3ft./sec.).

This slow moving mixture under the containment baffle is sufficientlyconcentrated that it is detectable by detecting means. Commerciallyavailable hydrogen fluoride composition detectors are sufficientlysensitive to react to concentrations of 1 part per billion parts byweight to 1 part per million by weight in 15 seconds to 1 minute. Thisthreshold is below the concentration of 20 parts per million by weightconsidered an immediate danger to life and health by the NationalInstitute of Occupational Safety and Health. As little as 50 parts permillion parts by weight is considered lethal. Secondary hydrogenfluoride detecting means includes hydrocarbon detectors and temperatureand pressure sensors. A massive release would be indicated by thepresence of hydrocarbon or a sudden or large temperature or pressurechange under an impingement baffle. For example, a temperature change of10° F. (5.5° C.) or more or a pressure change of 1 psi or more wouldindicate a vapor release.

Primary, composition detectors and secondary detectors are shown asdetector 110 associated with tank 10, detector 130 associated withreactor vessel 30, detector 150 associated with catalyst settler vessel50 and detector 170 associated with spent acid tank 70. It is understoodthat the drawing is schematic and an array of detectors may bedistributed within each containment baffle. Such an array wouldincorporate both primary, composition detectors and secondary detectorsincluding hydrocarbon detectors, thermocouples and pressure sensors.

Each detector produces a signal when activated by the presence ofhydrogen fluoride. Detector 110 produces signal 111 which is transmittedto valve actuator 113. Valve actuator 113 actuates quick open valve 115providing a flood of aqueous liquid from water supply 114 intocontainment baffle 12 via flood line 116. The aqueous liquid is water.Incorporated in the liquid water may be alkali agents, buffers andsurfactants to improve effectiveness in dissolving and neutralizinghydrogen fluoride. The water is passed via fog nozzle 117 which isrepresentative of a plurality of fog nozzles positioned aroundcontainment baffle 12. Fog nozzles are available which produce watermists having an average droplet size of 300 micron to 2000 micron andgreater. This droplet size provides a large amount of surface area forthe capture of hydrogen fluoride vapor.

The hydrogen fluoride dilute aqueous liquid is passed via drain line 15to vented sump 90 where it is collected. Vapor recoveries up to 90% havebeen demonstrated experimentally with water/hydrogen fluoride vaporratios of 6/1 to 40/1 by weight.

Likewise detector 130, signal 131, actuator 133, water supply 134, quickopen valve 135, flood line 136 and external spray head 138 are shown.Likewise detector 150, signal 151, actuator 153, water supply 154, quickopen valve 155, flood line 156 a, flood line 156 b, fog nozzle 157 andexternal spray head 158 are shown. Likewise detector 170, signal 171,actuator 173, water supply 174, quick open valve 175, flood line 176 a,a flood line 176 b, fog nozzle 177 and external spray head 178 areshown. The drawing is schematic and each vessel may contain a pluralityof fog nozzles and external spray heads.

Hydrogen fluoride dilute aqueous liquid is passed via drain lines 35, 55and 75 to vented sump 90 where it is collected. Sump 90 may be used incombination with ground containment means such as earthen, concrete andasphaltic dikes.

U.S. Pat. No. 5,073,674 to Olah incorporated herein by referencediscloses catalytic alkylation using liquid onium polyhydrogen fluoridecomplexes. These compositions show less volatility at alkylationconditions than anhydrous hydrogen fluoride. These complexes incombination are therefore more susceptible to recovery by water floodand are the Best Mode for carrying out the invention contemplated byinventors.

While particular embodiments of the invention have been described, itwill be understood, of course, that the invention is not limited theretosince many modifications may be made, and it is, therefore, contemplatedto cover by the appended claims any such modification as fall within thetrue spirit and scope of the invention. For example, hydrogen fluorideutilizing means is understood to include vessels for carrying outhydrogen fluoride manufacture, fluorocarbon manufacture, fluorination,and the aromatic alkylation process.

What is claimed is:
 1. Environmental safety apparatus for collecting anairborne release of hydrogen fluoride from hydrogen fluoride utilizingmeans comprising: a containment baffle defining a volume sufficient tosubstantially enclose said hydrogen fluoride utilizing means; at leastone hydrogen fluoride detecting means mounted within said containmentbaffle; flood means to substantially flood said containment baffle withan aqueous liquid; means responsive to said detecting means to activatesaid flood means; and means to receive said aqueous liquid from saidcontainment baffle.
 2. The safety apparatus of claim 1 comprising anarray of detecting means distributed within said containment baffle. 3.The safety apparatus of claim 1 wherein said flood means comprises aplurality of fog producing nozzles sufficient in number to substantiallyimmediately fog the entire volume of said containment baffle.
 4. Thesafety apparatus of claim 1 wherein said hydrogen fluoride detectingmeans comprises a composition analyzer.
 5. The safety apparatus of claim1 wherein said hydrogen fluoride detecting means comprises athermocouple.
 6. The safety apparatus of claim 1 wherein hydrogenfluoride utilizing means comprises an alkylation apparatus.
 7. Thesafety apparatus of claim 1 wherein hydrogen fluoride utilizing meanscomprises a containment vessel.
 8. The safety apparatus of claim 1wherein hydrogen fluoride utilization means is a transportation vessel.